In a conventional droplet ejection device for ejecting a liquid such as ink in a droplet state and performing a coating operation, a printing operation, or the like, a droplet ejection head (such as an inkjet head) has been used, in which droplets are ejected from nozzles by use of displacement of piezo elements. As for the droplet ejection head, a patent publication described below has been known.
An inkjet head described in Patent Publication 1 (U.S. Pat. No. 4,439,780) includes chambers including orifices for ejecting ink (corresponding to nozzles in the present embodiment), transducers (corresponding to piezo elements in the present embodiment) configured to expand and contract so as to change a content of each chamber by applying voltage, an ink reservoir for storing ink (corresponding to a liquid room in the present embodiment), and restricted openings (corresponding to restrictors in the present embodiment) through which the ink reservoir and the chamber are in communication with each other.
In the conventional inkjet head, ink is ejected in the chambers from the orifices by causing the transducers to expand and contract and applying pressure to the ink in the chambers. Then, the same amount of ink as the ejected ink is supplied into the chambers from the ink reservoir via the restricted openings. Note that, a flow-path area of each restricted opening is configured to be small in order to prevent the ink in the chambers from flowing back to an ink reservoir side when pressure is applied to the ink in the chambers by causing the transducers to expand and contract.
In the conventional inkjet head described in Patent Publication 1, when air bubbles enter the chambers, an ejection property of the ink from the orifices is lowered if the air bubbles are not removed. As a result, the ink may not be ejected from the orifices. In such a case, the ink in each chamber is flown out through the orifices with the air bubbles by applying pressure to ink in the ink reservoir and transmitting the increased pressure to the ink in the chambers. However, the conventional inkjet head has a small flow-path area of each restricted opening. Consequently, the increased pressure in the ink reservoir cannot be transmitted directly to the ink in the chambers. Thus, it may be difficult to bring the air bubbles out from the orifices with the ink.